Once upon a time, with older RC cars and NiCd batteries, you could just take the battery, plug it into a wall charger, and leave it. You would have to wait for several hours, or preferably leave it overnight, and your battery would be ready for use again. The method for charging a LiPo battery, however, is completely different. If you don’t select a higher-end charging station, you'll spend too much time and attention. If they're not charged properly, they can become a real safety hazard.
We recommend that you use a specifically LiPo compatible charger, because LiPo batteries require specialized care. LiPo batteries charge using a system called CC/CV charging, which stands for Constant Current / Constant Voltage. Essentially, the charger will keep the current – or charge rate – constant until the moment the battery reaches its peak voltage (4.2v per cell in a battery pack). It will then maintain that voltage, while reducing the current.
Don’t use the pulse charging method, which is only applicable to NiMH and NiCd batteries. If you try to charge a LiPo battery in this way it can have damaging effects, so it's important to have a LiPo-compatible charger.
Another reason why you do need a LiPo-compatible charger is balancing. Balancing represents the act of equalizing the voltage of each cell in a battery pack. LiPo batteries should be balanced in order to ensure each cell discharges the same amount. This will help with the performance of the battery. Balancing is also vital for safety reasons, but I'll get to that in the section on discharging.
Regardless of existence of stand-alone balancers on the market, we recommend buying a charger with built-in balancing capabilities, using a balance board. This makes the process of balancing more simple and requires one less thing to be purchased. Considering the price of chargers with built-in balancers coming down to very reasonable levels, we believe there is no reason you wouldn’t want to simplify your charging set up.
The majority of LiPo batteries have a connector called JST-XH on the balance tap. The great disadvantage of this connector is its lack of surface area, leading to an inability to get a good grip on the connector. That means it's more difficult to unplug from a balance board and the user usually just ends up pulling on the wires. This produces a risk to break the connector and potentially short out the battery.
In order to solve this problem, we recommend you to get Balance Protector Clips (or AB Clips). This is a great way to solve that problem. Their role is to clip around the balance connector and give a user more space to grab on to it. Balance Protector lips are not expensive and a great way to prevent balance connector fatigue.
In comparison to NiMH or NiCd batteries, a lot of LiPo batteries have to be charged rather slowly. If the routine charge of a 3000mAh NiMH battery is at four or five Amps, a LiPo battery of the same capacity should be charged at no more than three Amps.
Just as the C Rating of a battery determines what the safe continuous discharge of the battery is, there is a C Rating for charging as well. For the vast majority of LiPos, the Charge Rate is 1C. The equation works the same way as the previous discharge rating, where 1000mAh = 1A. So, for a 3000mAh battery, we would want to charge at 3A, for a 5000mAh LiPo, we should set the charger at 5A, and for a 4500mAh pack, 4.5A is the correct charge rate.
The most recommended and safest charge rate for most LiPo batteries is 1C, or 1x capacity battery in Amps. Regardless, there are an increasing number of LiPo batteries that are coming out these days that advertise faster-charging capabilities, like the example battery we had above. On the battery, the label says it has a “3C Charge Rate.”
Keeping in mind the fact that the battery's capacity is 5000mAh, or 5 Amps, the battery can be safely charged at a maximum of 15 Amps. As it is best to default at a 1C charge rate, always defer to the battery's labeling itself to determine the maximum safe charge rate.
Fireproof LiPo bag
Because of the potential for fire when using LiPo batteries, regardless of the likelihood, certain precautions should be taken. Although you should always have a fire extinguisher nearby, it won't entirely put out a LiPo fire. A fire extinguisher will simply contain the fire and stop it from spreading.
Our advice is to use a CO2 (Carbon Dioxide) extinguisher. This device removes oxygen from the burn site and cools down the battery and surrounding items. One more safety precaution is to charge the LiPo in a fire-resistant container. There is a great demand for LiPo Bags on the market today. These bags are expensive, but they are more portable than other solutions.
You never charge your LiPo batteries unattended. In case a fire does happen, you'll need to be there to react as quickly as needed.
Choosing the right charger
At this time, I consider the Kinexsis KX80 (pictured to the left) to be one of the best values on the market. It's a multi-chemistry charger, which means it can charge NiMH, NiCd, Lead Acid batteries, and LiPo batteries. It can even charge the newest LiFe batteries that some use for receiver packs in airplanes and cars.
It has a built-in balancer that handles up to 6S LiPo batteries and can charge up to six Amps. It's a great charger for the price. It's not as high-power as some LiPo users may need, though, since it only operates at 80 watts, meaning higher cell count batteries may not charge very fast on the KX80.
For the case in which you have to charge multiple batteries at the same time, we recommend the Dynamite Prophet Sport Quad 50W charger. It has all the capabilities of the KX80, but with four independent 50W charge ports. This provides you the capability to charge up to four batteries at one time.
For the case that you need more wattage, the Dynamite Prophet Sport Quad 100W is the way to go, with four 100W charge ports. For large capacity batteries, large cell counts, or higher charging rates, you may want to find a charger that operates on higher wattages. As mentioned, the KX80 AC/DC charger works on 80 watts (80W). Each port on the Dynamite quad charger is 50W or even 100W, if you choose that version.
In order to clear this up even further, let's look at how watts, Amps, and voltage work together. You can calculate the watts with following formula: Watts = Voltage x Amperage. Wattage, voltage, and amperage are intertwined. You can convert voltage to amperage and vice-versa.
This is important in determining what kind of charger you need. Let me show you how.
Let’s take as an example we have a 6S 5000mAh LiPo battery and we want to charge it at 1C, which would be 5A. If we have a KX80 AC/DC Charger, we can set up the charger to charge at 5A for a 6S battery. But when we go to charge the battery, the most it ever charges is at around 3.5A.
If we use the formula above, we can plug in our voltage (22.2V) and our Amperage (5A) and we will get this: 22.2v x 5A = 111W. The formula says that if we want to charge our 6S 5000mAh LiPo pack at 5 Amps, we would need a charger that is capable of delivering at least 111 Watts of power.
Parallel vs. Series Charging
It is our opinion that parallel charging can be very dangerous. Many experts from well-known battery manufacturers “consider parallel pack charging to be highly dangerous and should not be attempted even by experienced users”. What makes the problem with parallel charging (or even using your batteries in parallel) is that, when hooking up batteries in parallel, you are doubling the capacity of the batteries while maintaining the voltage of one of the individual batteries.
In other words, your charger, which normally monitors the battery while charging to prevent overcharging, can’t see all of the individual batteries' voltages. The charger can only see one.
One more disadvantage of parallel charging is the inequality of the batteries. In the case that two batteries (and the cells contained therein) were completely identical, parallel charging would be okay. This would mean that the batteries would have to have been from the exact same production lot, had the exact same chemical composition, age, charge history, and everything else. The fact is that you as a consumer will never be able to replicate those conditions, or even come close.
The question is what happens with batteries that are built in parallel? If you can match all those parameters to be identical, parallel charging is okay. Manufacturers tend to continuously monitor and test the materials that make up the cells at the factory. Each cell is marked with a UPC code that consists of the entire chemical makeup and history for that cell.
When a manufacturer assembles a battery, a computer scans and sorts the cells into compatible matches. Only in that case is it safe to parallel charge these cells. Regardless of that, when you charge a LiPo battery at home, even if it is already constructed in parallel, you don't need any fancy parallel charging boards. The work is already done for you and you simply need to charge it as you would a normal battery.
We also want to warn you not to use parallel charging cords. There is no safe way to use these. Parallel charging is always a risk. There can be found thousands of successful attempts to parallel charge batteries around the web. These are simply people that have not yet managed to burn their home down and every battery expert will confirm that.
Series charging is the safer of the two methods, meaning it's no less dangerous than straight-up normal charging. The only condition is to set up your charger the right way. For the case that you want to charge six single-cell LiPo batteries that are all the same capacity you can wire them up in series, set up your charger as if it were a six-cell LiPo, and balance charge your LiPos.
Charging LiPo batteries consists of making the charger individually charge each cell and making sure they are all kept at safe levels. For a single-port charger, series charging is the only safe way to charge multiple batteries at the same time, but wiring them up properly is pretty complex and not something a beginner should attempt.
The most recommended way to charge multiple batteries at the same time is to have a multi-port charger, like the Dynamite Prophet Sport Quad, mentioned above. If you have a need to charge many batteries at once, do the smart thing and purchase a charger (or chargers) that will fit your needs.
Discharging LiPo Batteries
In comparison to other types of rechargeable batteries, such as NiCd and NiMH, LiPo batteries will be permanently damaged if discharged below a minimum voltage. The voltage on a LiPo battery has to be maintained above 3 V or the battery will not accept a future charge.
The number of cells per battery doesn’t impact to this discharge limit, as the limit is per cell. LiPo batteries usually should only be discharged to 20% of their capacity to prevent the battery from dropping voltage unexpectedly and sustaining damage that can’t be fixed.
LiPo Battery Charging Safety
The following is a list with essential safety precautions for charging LiPo batteries:
- Never charge LiPos unattended.
- LiPo cells must not be punctured.
- You must pay attention not to short circuit the battery by plugging in connections backwards. This is particularly important if you soldered on a connector (XT-60, bullet, etc.) backwards and forgot to label the reversed orientation.
- LiPos that have been involved in crashes, dropped, or sustained some kind of physical trauma may be damaged internally and should be watched closely at the next charging.
- Batteries have to be charged in a well-ventilated area.
- LiPos have to be charged on a metal surface or inside of a LiPo storage pouch.
- Use the balance plugs.
- Try not to be aggressive with charge rate. In addition to shortening the battery’s lifespan, this can cause overheating and a possible fire.